Generation and trapping of a highly strained bicyclic alkyne: Tricycle [6.3.1.0(2,7)]dodeca-2,4,6-trien-9-yne

High-temperature bromination of 10-bromotricyclo[6.3.1.0(2,7)]dodeca-2,4,6, 9-tetraene (8) resulted mainly in the formation of two isomeric tribromides (16 and 17) whose dehydrobromination with DBU afforded the corresponding 9 ,10-dibromotricyclo [6.3.1.0(2,7)] dodeca-2,4,6,9-tetraene (14). Treatment of 14 with tert-butyllithium in THF at -78 degreesC produces the strained b icyclic alkyne (10) which is trapped by 1,3-diphenylisobenzofuran to give t wo isomeric cycloadducts 12a and 12b. The adducts 12a and 12b were found to readily rearrange to the isomeric ketones 19a and 19b upon chromatography. Upon treatment with potassium tert-butoxide, the adducts 12a and 12b under go base-catalyzed double bond isomerization to give four products 20-23. Fu rthermore, reaction of 14 with one and two mole of potassium tert-butoxide has been studied and the mechanism of the product formation is discussed wi th regard to either an allene or alkyne as a possible intermediate.